Decoding method

ABSTRACT

A decoding method for decoding information content in at least one data packet, which is transmitted from a sender to a receiver via a data link. The information is represented by a bit sequence, which is transformed into a transmittable redundancy version. The information is initially transmitted for a first time in a first data packet from the sender to the receiver. The information is represented by a first redundancy version, which is self-decodable. An incorrect receipt is confirmed by sending a confirmation from the receiver to the sender. The information is retransmitted at least a second time in a second data packet from the sender to the receiver upon receipt of the confirmation, wherein, for representation of the information, a second redundancy version is used, the selection of which is performed in dependence on a coding parameter, describing whether the redundancy version is self-decodable or not.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 11/661,006,filed Feb. 23, 2007, which was a §371 of PCT/EP2005/054578, filed Sep.15, 2005, which designated the United States; the application alsoclaims the priority, under 35 U.S.C. §119, of European patentapplications Nos. EP 04021970.1, filed Sep. 15, 2004 and EP 04027144.7,filed Nov. 15, 2004; the prior applications are herewith incorporated byreference in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The invention concerns a decoding method and a telecommunication devicefor performing that method.

Often for a better decoding result several transmissions of the samedata packet are combined. Combining data packets is already known forcommunication systems where packet transmission is employed. One exampleof such a transmission system is the so called E-DCH scheme (E-DCH:Enhanced Dedicated Channel, basically an improvement of the existingUMTS uplink channel) which is right now being standardized as anenhancement of the UMTS system (UMTS: Universal Mobile TelecommunicationSystem).

The outlines of the E-DCH scheme can be found in the 3GPP RAN 1technical report TR 25.896 v2.0.0 “Feasibility Study for Enhanced Uplinkfor UTRA FDD (Release 6)”, R1-040392, February 2004, Malaga, Spain.

This scheme is designed to make use of a HARQ (HARQ: Hybrid ARQ, HybridAutomatic Repeat reQuest) scheme. In this scheme packets aretransmitted, and if they are not received correctly, a retransmission istransmitted upon receipt of a negative confirmation of the receiver, aso called “not acknowledge” (NACK). If the receipt has been correct apositive confirmation is sent, the so called “acknowledge” (ACK). In thecase of more than one transmission of the same data packet, at thereceiver both the initial transmission and the retransmission is usedfor decoding the packet. Therein “soft bit decisions” making use of theinformation of both data packets is used. This means that to every bitof the data packet of transmission or retransmission a quantity isassigned which is correlated with the probability, whether the bit is 1or 0. The decoding is then done considering both quantities.

This gives a better performance, as if only the retransmission would beused without regarding previous transmissions (hybrid ARQ with selectioncombining).

In order to a proper function of this scheme as explained above, itshould be ensured, that both received transmissions actually relate tothe same transmitted (higher layer) packet i.e. both transmissions arederived from the same information content, the same “higher layer”packet (but may be transmitted using different packets on layer 1).Layer refers here to the OSI (Open System Interconnection) model. Due totransmission properties, which are considered in layer 1, therepresentation of information for a certain application, the applicationitself being taken care of in a higher layer) may be different fortransmission and retransmission.

There are several ways to ensure this: one is a so called synchronousretransmission protocol. In this protocol a retransmission is sent at afixed time interval after the initial transmission or also the previousretransmission, if more than one retransmission is foreseen. In this waythe receiver knows at which times it can expect retransmissions of agiven packet.

However, the receiver still does not know, whether two transmissions atcompatible times actually relate to the same packet, or whether alreadythe transmission of a new packet has been started. This is in particularthe case if the receiver is not able to receive all packets but missessome, e.g. due to interference. If the transmission employs softhandover (SHO), that means that more than one receiver tries to receivethe packets, it may well be that one receiver has not been able toreceive a packet, but another receiver has been able to do so andacknowledged the packet. In this case a new packet can be transmittednext. The receiver which did not receive the first packet has noknowledge on the acknowledgement send by the other receiver andtherefore must now somehow recognize that this new packet cannot becombined with any previously received packets.

In respect of the E-DCH a soft handover takes place, e.g. if a terminal,which has established a data connection with a first base stationapproaches a second base station. In a transition phase there is aconnection to both base stations, in order to ensure a smooth or softtransition when going from one cell, governed by the first base stationto the second cell, governed by the second base station.

For an easy recognition, it is further possible to introduce a so calledRetransmission Sequence Number (RSN) or retransmission counter:

This counter is reset (e.g. to 0) if a new data packet is transmitted,and it is incremented with each retransmission. If the receiver comparesthe difference in RSN with the difference in time (taking intoconsideration the synchronous retransmission protocol and the known timedifference between retransmission), the receiver can combine thereceptions if the differences in time an RSN match and not combine themif the differences do not match.

It is a problem according to the state of the art, that the value rangeof the RSN is at least as large as the maximum number of possibleretransmissions: Typically if a packet cannot be transmitted with amaximum number of retransmission this packet is dropped and the nextpacket is transmitted. The maximum number of possible retransmissionscan be quite high. This can cause an excessive amount of signalinginformation, as the RSN has to be transmitted with every packettransmission and retransmission.

SUMMARY OF THE INVENTION

Based on this state of the art, it is therefore an object of theinvention to provide a possibility of improving a transmission of datapackets, wherein a retransmission of data packets is foreseen.

It is a further task of the presented invention to present an improvedretransmission method.

This object is achieved by what is disclosed in the independent claims.Advantageous embodiments are subject of the dependent claims.

According to the invention a data packet is transmitted from a sender toa receiver. In the data packet information is contained, which isrepresented by bit sequence. For transmission this bit sequence istransformed into a redundancy version that is one out of more possiblerepresentations suited for transmission. In case the receiver does notreceive the data packet correctly, it sends a confirmation, e.g. a NACK,to the sender. Upon this receipt the sender retransmits the informationin a second data packet, which might be different from the first one.For this retransmission a second redundancy version is used, which mightbe different from the first one. The selection of the redundancy versionfor the second transmission is based on a coding parameter, whichdenotes whether the redundancy version is self-decodable, that meansdecodable only by itself or not.

This selection has the advantage that the selection of the redundancyversion can be done taking into account the transmission properties,e.g. whether the receiver has previous versions of the data packetswhich it can use for decoding. Thus better decoding results can beachieved. At the same time no or only little additional effort isperformed for additional signaling.

Further aspects and criteria of the selection of the redundancy versionare detailed in the description of embodiments and Figures.

The present invention gives also an enhancement of the “RetransmissionSequence Number” (RSN) concept, which allows reducing the value range ofRSN while still allowing it to be used to determine which packets tocombine, at least for most cases, in particular in those cases where thenumber of retransmissions does not exceed the maximum value of the RSN.The first and/or the second retransmission numbers according to thisapplication can be designed to be a “Retransmission Sequence Number”according to the previous description.

There may now be some cases where the receiver can now no longer tellwhether packets have to be combined, but these cases are rare enough andwill not severely harm the performance. It is more valuable to reducethe number of bits needed to encode the RSN, say from 3 bits to 2 bits,which gives a significant reduction of the resources needed to transmitthis “overhead” information along with the packet data.

BRIEF DESCRIPTION OF THE DRAWING

The sole FIGURE shows a connection between a terminal and a basestation.

DESCRIPTION OF THE INVENTION

In the FIGURE a terminal U is depicted, which has a connection E-DCH toa base station BS.

The terminal may be any communication device, e.g. as a mobile phone, aPDA (personal digital assistant), a mobile computer etc. The basestation may be any central unit in a communication system CS. Thecommunication system can be represented e.g. by a mobile communicationsnetwork such as UMTS (Universal system of mobile communication), a localarea network such as WLAN (wireless local area network) or a broadcastsystem.

The connection E-DCH may be any data link between the terminal UE andthe base station BS, wherein data packets are transmitted. Except of theEnhanced Uplink Dedicated Channel it may be the HS-DSCH (High-SpeedDownlink Shared Channel), or . . . or any other data link such as abroadcast connection.

The terminal UE sends data packets to the base station BS. The basestation acknowledges the correct or incorrect receipt with a ACK or aNACK, which is sent back to the terminal UE.

In case of a NACK, the terminal UE retransmits the data packet. As laidout above, the data packet is the same from the information content, butmay employ a different encoding e.g. a different subset of the codedbits.

In the following description, the retransmission numbers according tothis invention are abbreviated as RSN.

According to the invention the RSN concept used as follows: If a newpacket is being transmitted (i.e. at the first transmission of a newpacket), the RSN is reset to 0.

If a retransmission of a packet is transmitted, and the RSN is stillbelow its maximum value, then the RSN is incremented. If aretransmission of a packet is transmitted, and the RSN has alreadyreached its maximum value, then the RSN is not incremented but remainsat the maximum value in contrast to previous proposals. This has theadvantage, that the space needed for signaling can be limited to apreviously set value.

We name the maximum value of RSN as RSNMAX for the further discussion(RSNMAX can be a maximum retransmission number.

The receiver can combine a received packet with the previously receivedpacket, if e.g. one of the following conditions 1 or 2 holds. For thispurpose it will take into account also the RSN of the previouslyreceived packet (the last received packet) and the time difference sincethe reception of that packet (the time difference can be a delay timeconsisting of a number of retransmission time steps e.g. according tothe claims). Note that the time difference is identical to the number ofincrements of the RSN since that last packet, provided that no newpacked has been transmitted and that the limitation of RSN to RSNMAX hasnot happened yet.

A combination of the data packets is possible, if

1) the RSN is smaller than RSNMAX and the difference in RSN is identicalwith the difference in transmission time (in this case there was neitheran overflow of the RSN nor has a new initial packet been sent) or2) the RSN is identical to RSNMAX, the last received packet has beenreceived with the difference in time being at most RSNMAX and the RSN ofthat last packet plus the time difference is at least RSNMAX. In thiscase there may have been an overflow of the RSN, but the packet receivedcorresponds to the last received packet, otherwise the RSN would havebeen reset to 0 after that last packet, and would not have beenincreased to RSNMAX because the time difference since then is too small.The packets may be not combined for example in the following cases 3 or4:3) the RSN is smaller than RSNMAX and the difference in RSN is notidentical with the difference in transmission time (in this case therewas no overflow of the RSN and a new initial packet been sent, thereforethe data relating to the old packet can be safely deleted) or4) the RSN is identical to RSNMAX and the last received packet has beenreceived with the difference in time being more than RSNMAX. In thiscase the receiver cannot determine whether the actual and the lastreceived packets are to be combined, i.e. cannot determine whether therehave only been retransmissions of this packet been sent, or whetheralready a new packet and so many retransmissions of this new packet havebeen sent, so that the RSN has already reached RSNMAX. Therefore, inorder to avoid a potential mixing up of data of different packets, theinformation relating to the old packet will have to be deleted.

In the case that the RSN is identical to RSNMAX it is actually notpossible that the last received packet has been received with thedifference in time being less than RSNMAX and the RSN of that lastpacket plus the time difference is smaller than RSNMAX. Consequently,strictly speaking, the RSN of the last packet plus the time differenceneeds not necessarily be computed and compared to RSNMAX. However it iseasy to do and in this case some rare error cases may be detected, wherethe RSN has been decoded incorrectly. This is unlikely as the RSN willhave to be coded/protected suitably anyhow, but as the calculation is soeasy, it would be advantageous to do it and to exploit this extraconsistency check.

For a further explanation of the present invention, we will present somemore detailed examples by reference to the following Table 1:

T 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 RSN 0 0 1 2 3 3 3 3 3 33 3 0 1 2 3 3 3 3 RX 0 —  1f — 3 — — 3 — — —  3f 0 — 2 Hyp 0 1 2 0 1 2 01 2 3 3 0 1

The table 1 shows:

-   -   In the first line the time T (in units of transmission times        i.e. time difference of retransmission in the synchronous        retransmission protocol). The time T may be denoted in a fixed        number of time slots or so called TTI (time transmission        interval).    -   In the second line the actually transmitted RSN.    -   In the third line the received RSN, which is denoted as RX, if        no RSN has been received (e.g. due to interference), this        missing receipt is indicated by a dash (-).

Furthermore a “f” indicates that the buffer has been cleared i.e. thatthe receiver assumes, that the actually received packet cannot becombined with the previous one.

-   -   In the fourth line, for explanatory purposes, another potential        sequence of transmitted RSN is given to show whether it is        possible, that the same RSN has been received but a new packet        has already been sent.

According to the present example, at time 0 the RSN is set to 0 and apacket is transmitted.

At time 1 a new packet is transmitted and the RSN is reset to 0 again.This RSN is however not received by the receiver (-).

At time 2, a retransmission of the packet transmitted already at time 1is transmitted. The receiver recognizes that this packet is not to becombined with the previously received packet, i.e. the packettransmitted at time 0, because the actual RSN is smaller than RSNMAX andthe difference of the actual RSN minus the last received RSN (which was0 at time 0) is 1−0=1 does not match the time difference which is 2(time 2 minus time 0). This is according to case 3 set out above. Notethat if still a retransmission of the packet from time 0 was sent, thenthe RSN would by now have been incremented to 2 as indicated in the lineHyp. Therefore the receiver can rule out this case, this means, it doesnot perform a combination.

At time 3 a retransmission is transmitted, but not received.

At time 4 a retransmission is transmitted, the RSN is increased andreaches RSNMAX. The receiver detects this, the time difference since thelast received RSN is 2, and the last received RSN (1) plus this timedifference gives 3, which is at least RSNMAX. Therefore the packet iscombined with the last packet at time 2 according to case 2.

At time 5 to 6 retransmissions are sent, the RSN stays at RSNMAX.

At time 7 a retransmission is sent, still the RSN stays at RSNMAX. Thereceiver combines this packet with the previously received packet attime 4 according to rule 2: RSN is RSNMAX, the time difference is 3,i.e. at most RSNMAX and the previous RSN plus the time difference is 6i.e. at least RSNMAX. If a new packet had been sent since time 4, theRSN would have been reset and could have increased at most to 2 sincethen as shown in the line Hyp.

At time 8 to 10 retransmissions are sent, the RSN stays at RSNMAX.

At time 11 a retransmission is sent, still the RSN stays at RSNMAX. Thereceiver does not combine this packet with the previously receivedpacket at time 7 according to rule 4: RSN is RSNMAX, the time differenceis 11−7=4, i.e. larger than RSNMAX. A new packet could have been sent attime 8, the RSN would have been reset and could have increased to 3since then as shown in the line Hyp. Therefore the receiver does notknow for sure whether the packet received at time 11 can be combinedwith the packet at time 7 or not, therefore it has to make aconservative assumption i.e. not combine the data. This is indicated bythe letter f at time 11 in line 3.

At time 12 a new packet is sent and received and RSN is reset to 0.

At time 13 a retransmission is sent but not received and RSN isincremented to 1.

At time 14 a further retransmission is sent and received and the RSN isincremented to 2. The receiver combines this packet with the previouslyreceived packet at time 12 according to rule 1: The RSN 2 is stillsmaller than RSNMAX and the difference in RSN 2−0=2 is identical withthe difference in transmission time 14−12=2. The line Hyp shows that ifa new packet had been sent (but missed) at time 13 than the RSN wouldnot be 2 but 1.

Up to now embodiments have been detailed, which are already applicable,if an identical data packet has been retransmitted.

Furthermore, it is possible, that in a HARQ system for the same contentnot identical packets (this is called “chase combining”) but e.g.differently encoded packets are sent, known e.g. as different redundancyversions (also called “incremental redundancy”).

In this case, also an indication which redundancy version is transmittedwith a given packet can be used. This would additionally increase theoverhead information. Therefore the signaling of the redundancy versioncan be performed implicitly with the RSN or implicitly with the time atwhich the packet is sent. Both transmitter and Receiver can calculatethe applied redundancy version (RV) from either the RSN or transmissiontime (or equivalently to the transmission time a transmission framenumber or connection frame number, also called CFN, the latter will beused in the following without intention to restrict others.)

For the improved RSN as presented in this invention, the determinationof the RV can be done as follows: For the values of RSN below RSNMAX,the RV can be calculated from the RSN. However, when RSN reaches RSNMAX,it will remain at this value for all the remaining retransmissions ofthe packet. Therefore in this case, it is better to calculate the RV notfrom RSN but from the CFN. In summary, according to this aspect of theinvention the RV is calculated from the RSN if RSN<RSNMAX and from CFNif RSN=RSNMAX.

In a further embodiment of the invention, the relation of RV to RSN canbe signaled from the receiver to the transmitter before of thetransmission, in particular for RSN<RSNMAX.

In a further embodiment there may be a default relationship predefinedbetween transmitter and receiver, which can be replaced by a signaledrelationship. The relationship can be signaled e.g. for some values forRSN, in particular for the most often used ones, while for others, e.g.the less often used ones, default values are used. Alternatively, ifdifferent packet sizes or coding schemes can be used by the system (thisapplies in particular for AMC (Adaptive Modulation and Coding) schemes),default values can be used for some sizes/schemes and explicit signaledRV values can be used for others.

Furthermore there are coding methods, which distinguish between twoclasses of coded bits, namely systematic bits and parity bits. Basicallysystematic bits correspond to the information to be transmitted whileparity bits provide redundancy information. In such cases it may bebeneficial to emphasize systematic bits for the initial transmission,but parity bits in at least some of the retransmissions. In this case itis possible to not signal the fact to emphasize systematic bits in theinitial transmission. This can save some transmission bandwidth forsignaling the RV to RSN relation. Furthermore, it may even be sufficientto always use a predefined RV for the initial transmission and onlyprovide explicit signaling of RV to RSN relations for (some of the)retransmissions. Furthermore, for the case RSN=RSNMAX, it can also bebeneficial to emphasize systematic bits. This is in particular true forlow encoding rates (i.e. there is a significant redundancy available ina transmitted packet). Then it is possible to also not signal explicitlyto emphasize systematic bits for the case RSN=RSNMAX.

The following examples deal with a retransmission of redundancyversions. One important aspect is how the selection of the redundancyversion is performed, as this often influences the effectiveness of acombined decoding of a data packet as transmitted originally takentogether with a retransmission, which is in this case a redundancyversion.

The exact selection of the redundancy version depending on the RSN willbe detailed in the following sections. It will be apparent to thoseversed in the art, that these aspects can be advantageously combinedwith any aspect of the previously disclosed embodiments. As well, theseaspects can be applied independently.

It has been proposed, to select different redundancy versions based on aso called RV index (Redundancy Version Index). The RV index basicallydefines all the parameters, which are needed to define a specificredundancy version. This indexing enables an easy reference to aparticular redundancy version, because only a single parameter i.e. theRV index needs to be specified. This specification is particularlytransmitted or “signaled” from the terminal UE to the base station BS.The general aspects such as the general signaling architecture regardingE-DCH are discussed in R1-041408 3GPP TR 25.808 V0.2.3 (2004-10)Technical Report 3rd Generation Partnership Project; FDD EnhancedUplink; Physical Layer Aspects.

One proposal for a relation between the RV index and derived parametersis given in R1-041354, Editor (Siemens), “CR 25.212—Introduction ofE-DCH”, November 2004, Shin Yokohama, Japan in its section “4.8.4.3 HARQRate Matching Stage”.

In particular the relation of the parameters s and r to the E-DC-RVindex is relevant:

The parameters of the rate matching stage depend on the value of the RVparameters s and r. The s and r combinations corresponding to each RVallowed for the E-DCH are listed in the following Table 1. The firsttransmission attempt of a transport block shall use a RV that emphasizesthe systematic bits (RV with s=1). Higher layer signaling is used tocontrol the number of redundancy versions the UE shall use.

TABLE 1 RV for E-DCH E-DCH RV Index S r 0 1 0 1 0 0 2 1 1 3 0 1The following parameters are used:

N _(sys) =N _(p1) =N _(p2) =N _(e,j)/3

N _(data) =N _(e,data,j)

r _(max)=2

The exact way how these parameters are used to determine the actuallyused rate-matching pattern are described in the above cited section ofR1-041354, Editor (Siemens), “CR 25.212—Introduction of E-DCH”, November2004, Shin Yokohama, Japan. This way can be applied also for the variousembodiments presented here.

In particular, the following two sections of this document shows, howthe rate matching pattern is derived. The first citation, chapter4.2.7.5 “Rate matching pattern determination” deals with the exactdetermination of the rate matching pattern based on the parameterse_(plus), e_(minus) and e_(ini). Of these parameters e_(ini) describesthe initial error between the current or actual and the desiredpuncturing ratio, e_(plus) a stepwidth for changing the error and,e_(minus) another step width, used in the rate matching algorithm. Thesection Chapter 4.5.4.3 “HARQ Second Rate Matching Stage” describes howto calculate these parameters from the input parameters N_(sys),N_(data) and r_(max), wherein N_(sys) denotes the number of systematicbits, that is bits carrying information in contrast to parity bits usedfor encoding, N_(data) denotes the total number of bits, i.e. paritybits and systematic bits and r_(max) denotes the maximum value of r plusone.

In Chapter 4.5.4.3. from this document shows how the parameters, inparticular e_(plus), e_(minus) and e_(ini) for the algorithm in section4.2.7.5 are set:

The parameter s specifies whether the RV is self decodable, this meansdecodable if only this RV is considered. Decodable means in thisrespect, that the information content of the data packet, represented bythe redundancy version can be found out. If s=1, then when puncturingduring rate matching the so called systematic bits are prioritized overthe parity bits of the turbo code. Such a redundancy version istypically self decodable, that means, that it can be decoded by itself,unless of course the reception is too noisy. This is not the case whens=0 (parity bits are prioritized), where it can happen that a RV cannotbe decoded by itself, even in the absence of noise, but only togetherwith another RV. Therefore the first transmission of a packet shouldalways be self-decodable, i.e. employ s=1. During soft-handover (SHO) itmay happen, that one base station does receive the packets from themobile station up to a certain time, while another base station receivesthe packets after that time. This happens, if the instantaneous pathloss to the second base station becomes better than the path loss to thefirst one, which can happen easily due to fast fading. Path loss is thedegradation of a signal transmitted over a certain connection betweene.g. a terminal and a base station. The signal takes a certain way, thepath. Due to reflection, interferences etc it is subject to adegradation.

If the path loss to the second base station becomes better, it isadvantageous, if all the redundancy versions are self-decodable, as Thesecond base station might otherwise not be able to immediately decodethe packets after such a switch, as it might not have received theinitial transmission of a data packet, which is self decodable, but onlylater transmissions, which are by itself not self decodable:

This intention is also covered in the sections 4.2.7.5 and 4.5.4.3described above.

The inventors have found out, that surprisingly this means notnecessarily, that s=1 should be selected for every RV, if the connectionor data transmission is currently in SHO. The reason is, that s=0 onlycreates a non-self-decodable RV if puncturing is applied as describedabove. By puncturing the canceling of individual bits is described.Puncturing is done in order to reduce the overall number of bits, e.g.to adapt the overall number to a fixed capacity of a transmission. Thepuncturing of bits is done such, that no or only as little as possibleinformation is lost. Therefore often mainly parity bits are punctured.

If now repetition is performed, then all coded bits are transmittedanyhow, some of them are even repeated. Therefore s=0 can be safelyselected. In this case s=0 simply selects another redundancy versionthan s=1.

Using different RVs enhances the performance (so called incrementalredundancy (IR)) and the more different RVs can be selected the better.So the general rule to use s=1 in soft handover as given in the citationis actually not beneficial in this case but should be modified for thecase of repetition.

Therefore according to an advantageous embodiment the selection ofredundancy versions is based not only on the RSN but also on the factwhether puncturing or repetition is used for rate matching.

Another criterion which is taken into account additionally oralternatively is the coding rate. The coding rate is the number of bitsbefore the coding divided by the number of bits after coding and afterrate matching. Rate matching is the puncturing or repeating of bits inorder to achieve a desired final number of data in a certain timeinterval or correspondingly a desired data rate.

Typically, for E-DCH, so called “turbo codes” are used for coding of thepayload data. Payload data are the data actually carrying information,in contrast for data used for signaling etc. These turbo codes have acode rate of (approximately) 1/3 i.e. for every bit to be coded threecoded bits are generated, namely one systematic bit and two parity bits.If the code rate (after rate matching) is smaller than 1/3 thenrepetition is used during rate matching, if the code rate is larger than1/3 then puncturing is used. Therefore the decision which RVs to use,and in particular whether to use s=0 can be based advantageously on the(coding) rate.

In this context it should be noted, that the code rate of a turbo codewithout rate matching is not exactly 1/3 but slightly lower, becauseadditionally so called “termination bits” are appended at the end of theencoded data. However, for the purpose of the embodiments described inthe context of this application, this difference is small enough to beirrelevant. Therefore, in the detailed embodiments it is possible toeither compute the coding rate taking the termination bits into accountor not. The result will generally be equal.

According to a further advantageous embodiment the following selectionof RVs based on the RSN and the code-rate is realized:

TABLE 2 Relation between RSN value and E-DCH RV Index coding rate rate ≧⅚ or RSN ⅓ < rate < ½ ½ ≦ rate < ⅚ rate ≦ ⅓ value E-DCH RV Index E-DCHRV Index E-DCH RV Index 0 0 0 0 1 2 3 1 2 0 2 3 3 └TTIN/ └TTIN/ └TTIN/N_(ARQ)┘ mod 2 *2 N_(ARQ)┘ mod 3 N_(ARQ)┘ mod 4

In table 2 the redundancy version Index for the E-DCH is shown forvarious coding rates and different retransmission sequence numbers RSN.

The E-DCH RV Index is computed from the RSN value, the used coding rateand, if RSN=3, also from the TTIN (TTI(time transmissioninterval)-number). For UMTS, if choosing 10 ms for a TTI, then the TTInumber is equal to the connection frame number CFN, for 2 ms TTI wedefine

TTIN=5*CFN+subframe number

where the subframe number counts the five TTIs which are within a givenCFN, stating from 0 for the first TTI to 4 for the last TTI. In otherwords, a subframe has for UMTS a length of 5 TTIs.

NARQ is the number of Hybrid ARQ processes that is how manytransmissions of individual data packets are performed in parallel. E.g.there is the transmission and retransmission of a data packet A. At thesame time transmission and retransmission of data packet B or furtherdata packets has already begun. The usage of the TTIN instead of the CFNis necessary, if a CFN contains more than one TTI in order todistinguish the TTIs within one CFN. This depends on the set up of theindividual data connection and the system within which the dataconnection is established. Therefore, the conditions can be generalizedfor other numbers of TTIs contained in a frame. The division by thenumber of NARQ, the number of ARQ processes, is necessary, because aretransmission will not be scheduled immediately after the previoustransmission, but only after reception of the correspondingacknowledgement (ACK or NACK). As explained above, in the meantime datapackets are transmitted using different HARQ processes.

As can be seen when comparing the last and the second column of Table 1above, E-DCH RV index is always chosen so that s=1 (i.e. E-DCH RV indexis 0 or 2, compare Table 2 above) is used in the second column. In thelast column which is used if the rate is smaller than 1/3, i.e. forrepetition, s=0 is used as well (E-DCH RV index 1 and/or 3).

Therefore, according to a further embodiment s=1 for 1/3<rate<1/2 isused as shown in table 2. According to another embodiment s=0 is notused, even if the data link or the data transmission is not in SHO. Inthis way, it is not necessary to establish a common understandingwhether SHO is used or not, which facilitates e.g. the signaling for thefollowing reasons:

Because the initiation of SHO always is somewhat delayed due to thedelay of the associated signaling, and because this signaling delay isnot necessarily equal for the signaling from the RNC (radio networkcontroller), from where the handover is typically initiated, to the basestations and the terminals or mobile stations, a perfect synchronizationof a common understanding is cumbersome. By the above embodiment thisnecessity of determining whether a SHO is currently performed isavoided.

Selecting only two RVs for this case is not disadvantageous as it wasconsidered before, because for these rates two RVs are sufficient totransmit: Via two retransmissions, all bits which are generated by theturbo coder can be transmitted: For rate 1/2, after rate matching, allsystematic and half the parity bits are transmitted in one RV in theother RV, again all systematic and the other half of the parity bits aretransmitted. Therefore the usage of a non-self-decodable RV, which couldtransmit even more parity bits, is not necessary for this code rate butonly for higher code rates. The inventors have found out that prior artmethods would be disadvantageous in the aspect of systematic bits,because in general the systematic bits should be emphasized more thanthe parity bits, also when taking multiple RVs together.

Therefore only for higher code rates than 1/2, we propose to use s=0,i.e. non self-decodable RVs for the retransmission. In particular, if1/2≦rate<5/6 we propose to use one non self-decodable RV, see the middlecolumn in table 9. At code rate 2/3 the first RV, which isself-decodable contains all systematic bits and 1/4 of the parity bits,the second RV, which is non-self-decodable contains purely parity bitsi.e. 3/4 of the parity bits. Therefore, up to rate (2/3), it is possibleto transmit all bits with two redundancy versions. At higher rates, itis necessary to use more than one non-self-decodable RV: If the coderate is one, only the systematic bits are transmitted in the initialtransmission, the first and second retransmissions contain each 50% ofthe parity bits. So one non-self-decodable RV is ideal for Rate 2/3 andtwo non-self-decodable RV are ideal for rate 1. As 5/6 is the arithmeticmean of 2/3 and 1, we propose to use this value for the transitionbetween one and two non-self-decodable transmissions. Obviously otherthresholds are possible as well, down to 2/3 as 2/3 is the maximum ratewhere all parity bits can be transmitted with on self-decodable and onenon-self-decodable transmission. Likewise the threshold of rate 1/2 canalso be set somewhat higher, e.g. at the arithmetic mean between 1/2 and2/3 which is 7/12 or any value between 1/2 and 7/12. Furthermore it wasdecided that the UE (User Equipment, a synonym for mobile station)should only use a given maximum data rate when in Soft Handover. Thereason is that mobile stations in soft handover will create interferencein two cells, so limiting their data rates beneficially influences thesituation in two cells. At this maximum data rate a certain coding ratewill apply. So in an embodiment of this invention, the transition pointi.e. the minimum coding rate at which also non-self-decodabletransmission are used, can be selected to correspond to the maximum datarate which is admissible in SHO.

In the right column, for code rates above 5/6, as was show above twonon-self-decodable RVs are proposed, see table x.

As stated above, the RVs are explicitly allocated to the first threetransmissions, where RSN<RSNMAX. If RSN reaches RSNMAX, which is 3 inthe example given above, the Redundancy version is calculated based onthe TTIN. This has the advantage, that different RVs are used forsuccessive transmissions, even if always the same RSN (i.e. RSNMAX) isused. Only for the first transmission with RSN=RSNMAX, it would beadvantageous to select the optimum RV, however then always this RV wouldhave to be used after RSN reaches RSNMAX, which is clearly undesirable.For the different rates some care needs to be taken, when selecting theformula that selects the RVs, this is detailed below:

If 1/3<rate<1/2, then only self-decodable RVs are used, so only theseshould be selected as well for RSN>RSNMAX. This is realized by└TTIN/NARQ┘ mod 2*2 in table x above.

If 1/2≦rate<5/6 (or generally in the middle column), one nonself-decodable transmission is needed. Still the systematic bits shouldbe prioritized, therefore two self-decodable RVs are used. For RSN=1 theE-DCH RV index 3 is selected, while for RSN=3, via the formula, the RVs0, 1, 2 are selected cyclically. In this way some further gain can bereached, as different non-self-decodable RVs are used for RSN=1 andRSN=3, this gives some additional IR gain. This is realized by└TTIN/NARQ┘ mod 3 in table x above.

If the rate≧5/6 (or 2/3 as explained above), then two non-self-decodableRVs are necessary to cover all parity bits. In order to also emphasizethe systematic bits in this case, we propose to use 4 RVs for RSN=3, twonon-self-decodable ones, and two (not only the minimum of 1)self-decodable RV. This is realized by └TTIN/NARQ┘ mod 4.

Here └ ┘ means rounding down to the largest integer, which is not largerthan x, also sometimes called floor(x) or int(x).

In the following embodiments a further, different, enhancement to theRSN scheme is employed, which can again be used either in combinationwith or independent from the other enhancements presented in thisinvention.

In R1-041339, Panasonic, Downlink signaling related issues for EnhancedUplink, November 2004, Shin Yokohama, Japan it was proposed, that aterminal UE should retransmit the initial redundancy version, if theE-DCCH data could not be decoded. The E-DCCH carries overheadinformation related to the payload-data, e.g. the used transport formati.e. the number of payload bits, and is necessary to decode thepayload-data. So if the base station could not decode the E-DCCH it willnot be able to make any use of the data transmitted on E-DCDCH. The basestation can determine that the E-DCCH was not detected correctly e.g. ifa CRC (cyclic redundancy check is appended to the E-DCCH data. If thebase station cannot make use of the first RV, then in R1-041339,Panasonic, Downlink signaling related issues for Enhanced Uplink,November 2004, Shin Yokohama, Japan it was proposed to retransmit thefirst RV again, in order to make sure that the first RV which isactually available for the base station is a self-decodabletransmission. In this document several proposals are made how this issignaled to the mobile station, e.g. by introduction of a third stateapart from ACK and NACK. In the context of the described embodiments theexact way of signaling is not critical, therefore any signaling used ina HARQ process can be applied.

In the frame of this application this signaling is called CNAK(Control-NACK). However, this document does not disclose any informationhow the re-selection of the first RV shall be realized in conjunctionwith the RSN scheme.

In this document in particular the section “Node B reception scenarios”is relevant, in particular the citation below, which starts at the thirdparagraph of this section:

The table below shows 3 different scenarios, which can occur when UEsends the initial transmission of a data packet. The second column inthe table describes the reception status at Node B for each scenario,the third column shows the preferred UE behavior in such situation.

UE behavior depending UE transmission Node B reception status on Node Breception 1 E-DPCCH sent with Node B decodes E-DPCCH, but UE retransmitsself-decodable self-decodable RV CRC of E-DPCCH fails RV of the datapacket. 2 E-DPCCH sent with Node B successfully decodes E- UE sends nextRV of the data self-decodable RV DPCCH, CRC on E-DPDCH fails packetaccording to the RSN 3 E-DPCCH sent with Node B successfully decode bothUE sends next data packet self-decodable RV E-DPCCH and E-DPDCH

In case the E-DPCCH cannot be decoded correctly, as listed as the firstscenario in the table, Node B cannot process the data received onE-DPDCH. A decoding of the received data is not possible and thereforeNode B discards the data. In our view it would be beneficial to transmitthe self-decodable RV again in such a situation. When UE sendsretransmissions according to the specified RV sequence, a decoding ofthe data packet is only possible after the transmission of the nextself-decodable RV, which may lead to an increased delay. Therefore weprefer to retransmit the self-decodable RV (initial transmission) insuch a scenario.

Scenario 2 describes the case when Node B decodes the E-DPCCH correctly,but the CRC on the E-DPDCH fails. Here Node B can use the receivedenergy on the E-DPDCH when combining it with further retransmissions.Therefore UE shall retransmit according to the specified RV sequence inthis case. We propose that the UE behavior is different depending onwhether the 1st or 2nd scenario has occurred.

There are basically two possibilities: One possibility would be toassign the first RV not only to RSN=0 but also to RSN=1 in this case,consequently, the next RVs would also be shifted to the respective nextRSN-value. While this approach is feasible, there is a better approachused in an embodiment:

If the mobile station receives a CNAK, then the next transmission issent again with RSN=0 and consequently with the first, self-decodableRV. At first sight this may seem to imply that the RSN protocol asdescribed above could no longer be used in this case. However, it can beenhanced to also support this case: Both base station and mobile stationare aware of this situation via the CNAK signaling. Both can thereforetake this fact into account for the RSN-protocol. Furthermore, the basestation may anyhow decide to flush the soft buffer as it could not makeuse of the first transmission, this is already in accordance with thehandling of the RSN-protocol. If this happens in Soft-Handover, thenother base stations are typically not aware that the first base stationhas transmitted a CNAK. However, due to the RSN-protocol they can detectthat a new RSN=0 transmission is sent and flush their soft buffer. Whileflushing the buffer is not strictly necessary in this case, it has theeffect that the other base stations become aware of the fact, that theRV sequence is reset, and will therefore use the correct RV. Otherwise,these other base stations would use a wrong RV, consequently they wouldnot have any chance to decode the packet, this would be a waste ofresources. Even if one of the other base stations in soft handover coulddetect the packet correctly already for the first transmission, the RSNprotocol still works fine: Then this base station sends an ACK at thesame time when the first base station transmits a CNAK. The mobilestation will then transmit the next packet, as usual using RSN=0. Thefirst base station will not be aware of the fact, that the second basestation has acknowledged the first packet and therefore is not awarethat a new packet is transmitted. However, as it will anyhow flush thebuffer from the first packet it does not matter whether now the first orthe next packet is transmitted.

Even if the mobile station or the terminal UE erroneously misinterpretsthe CNAK as an ACK, the base station can still correctly receive thenext packet. The first packet is lost in this case, but not due to theenhancement of the RSN-protocol but simply due to the false reception ofthe ACK. This error case is already possible without the RSN-protocolenhancement, when a NAK is miss-interpreted as an ACK, i.e. the enhancedRSN protocol does not cause any further degradation.

This invention has presented enhancements to the RSN. It should be notedthat there are also other possibilities to provide similar functionalityby other means or somewhat different signaling. One such proposal is theNDI (New Data Indicator). The NDI is incremented modulo a maximum valuefor every new packet but is identical for retransmission of a packet.The NDI scheme may be more robust in cases where there are manyretransmissions, because then the NDI is only incremented seldom andthere is less risk that it becomes no more unambiguous (e.g. due to wraparound).

According to a further aspect of this invention, either the RSN or NDIscheme can be used depending on properties of the connection. That meansthat even in a single connection sometimes RSN and sometimes NDI can beused depending on the property. Such properties may include the factwhether the connection is or is not in Soft Handover, or the used packetsize or coding rate.

In a preferred embodiment the selected property can be determined by thetransmitter and receiver without additional explicit signaling. In thiscase no extra signaling overhead is introduced.

It will be apparent to those versed in the art, that the presentedinvention can be combined beneficially by combining aspects presented inthis application with one another or with other known procedures. Theinvention which was described by example above is therefore consideredto be also applicable to those cases. In particular the examples and thedescription should not be understood to limit the scope of theinvention.

In the following further examples, explanations, embodiments andvariants of the present invention are given:

In the last meeting substantial progress regarding the HARQ definitionfor E-DCH was made. An important agreement was to have a synchronousprotocol with synchronous retransmissions and to have HARQ with IR andChase combining.

Further while operating IR it was agreed that the redundancy versionsare taken in a given order and that the first transmission alwaysemphasizes the systematic bits (s=1). For retransmissions in non SHOboth emphasizing and non emphasizing of systematic bits should bepossible (s=0 or s=1).

Another agreement for SHO was that the utilization of transmissionsalways emphasizing the systematic bits (s=1) is generally considered tobe beneficial.

Starting from these facts and the agreement that the RV may be linked tothe CFN for some E-TFCs and explicitly signaled for other E-TFCs thiscontribution proposes a solution for the signaling of the HARQ relatedinformation.

HARQ Related Signaling Information

The HARQ related signaling information is transmitted with every E-DCHpacket transmission together with the E-TFC information. Its function isto inform the Node B about the used redundancy version (Xrv value)needed for the de-rate matching as well as to trigger the flushing ofthe Node B soft buffer.

The redundancy versions and the ordering in which the redundancyversions are applied should be controlled by the network e.g. throughhigher layer signaling or it can be specified for every TFC using afixed mapping rule. The rule is known to both the UE and the network andcan implemented “hard-wired”. In our view for each TFC three redundancyversions (one for the initial transmission, one for the first and onefor the second retransmission) should be specified or signaled fromhigher layers.

In the following due to the different requirements regarding thereliability of the new data indication and the different link efficiencygains for the RV selection in SHO and no SHO we separate the discussionfor both cases.

Signaling in Case of No SHO

In case of no SHO we propose a 2 bit RSN as described in R1-040958,Ericsson, “E-DCH Physical Layer Hybrid ARQ Processing”, Prague, CzechRepublic, August 2004, where it is disclosed to include a RSN in uplinksignaling and derive the Redundancy Version based on the RSN.

This including of the RSN in signaling has also been described above inthe context of the introduction of the RSN.

Thus the applied redundancy version is signaled from the UE to the NodeB. Additionally the RSN provides the functionality of new dataindication (in case the RSN=0 the soft buffer is indicated to beflushed). The RSN is incremented with every retransmission and set to 0with every initial transmission. In case the number of retransmissionsexceeds two the RSN is set to 3 for all further retransmissions. Thishas the advantage that the number of bits for the RSN can be lower thanlog 2(N max) without losing IR gain since the number of different RVs istypically lower than the maximum number of transmissions N max. ForRSN=3 the RV selection is CFN based to achieve further gain.

Signaling in Case of SHO

As described in R1-040906, Motorola, “Synchronous HARQ and reliablesignaling during SHO (Enhanced Uplink)”, Prague, Czech Republic, August2004 in case of SHO specific TFCs are chosen by the UE. Generally theSHO TFCs provide lower rates. For lower rates it was already shownduring the study item phase that the IR link efficiency gain compared toChase combining is around 0.3 dB. However the performance differencebetween different IR schemes and also between IR schemes with differentRV orderings is negligible small, as it has been shown in R1-040719,Qualcomm, “Link Performance with different RV for Low Data Rates”,Cannes, France, June 2004.

Consequently to achieve the best performance also in SHO we propose touse specific TFCs together with IR. To specify an explicit rule for theRV selection is not reasonable due to the negligible differences of theIR schemes. Therefore we propose to do the RV selection implicitly andbased on the CFN similar as described already in several othercontributions [2,3].

In SHO then the 2 bit RSN as described for the no SHO case is no longerneeded and can be reused. Keeping in mind that the most important issuefor the HARQ related signaling in SHO is to avoid Node B buffercorruption we propose to reuse the 2 RSN bits as a 2 bit NDI. Incontrast to the RSN, which is incremented per retransmission, the NDI isincremented at the UE with every initial transmission. Compared to theRSN the NDI provides a higher reliability especially in case theresidual BLER after the first retransmission is targeted to 1%).

SUMMARY

In this document we propose to use only 2 bits for the HARQ related ULE-DCH signaling information used to provide the new data indication andthe RV selection functionality.

Depending on the chosen TFC the counter is incremented on a perretransmission (=RSN) or a per initial transmission basis (=NDI) tosupport the NDI or RV selection functionality as good as possible.

Background for this solution is the given fact, that in case of SHO theNDI reliability is much more critical than in non SHO and that the RVselection in non SHO has much more influence on the performance than inSHO.

Further the proposal comprises also the RV selection in SHO, which isdone implicitly using the CFN e.g. as described in [2,3]. In case of noSHO the RVs for the initial transmission and the first and secondretransmission is signaled by the network whereas the actual usage isindicated by the UEs RSN.

Abbreviations/Acronyms Used in the Description:

-   E-DCH: Enhanced Dedicated Channel, basically an improvement of the    existing UMTS uplink channel.-   E-DCDH: Enhanced Dedicated Data Channel, carries the payload-data of    E-DCH.-   E-DCCH: Enhanced Dedicated Control Channel, carries overhead data    (L1 signaling) for E-DCDCH.-   IR: Incremental Redundancy-   SHO: Soft Handover-   CFN: Connection Frame Number-   E-TFC: Enhanced Transport Format Combination-   UE: User Equipment, mobile station.-   log 2: logarithm base 2-   UL: Uplink-   RSN: Retransmission Sequence Number-   RSNMAX: Maximum value of Retransmission Sequence Number-   TTIN: TTI-number-   TTI: Transmission Time Interval-   CFN: Connection Frame Number-   ARQ: Automated Retransmission reQestHARQ: Hybrid ARQ-   ACK: Acknowledge-   NACK: Not Acknowledge-   └x┘: floor(x) i.e. the largest integer which is not larger than x.-   RV: Redundancy Version-   NARQ: Number of Hybrid ARQ processes-   UE: User Equipment, a synonym for mobile station or terminal

1. A method of transmitting an information content contained in at leastone data packet transmitted from a sender to a receiver via a data link,wherein the information is represented by a bit sequence that isenclosed into a transmittable redundancy version, the method comprisingthe steps of: a) initially transmitting the information for a first timein a first data packet from the sender to the receiver, wherein theinformation is represented by a first, self-decodable redundancyversion; b) receiving a confirmation confirming an incorrect receiptfrom the receiver at the sender; c) retransmitting the information atleast one first time in a second data packet from the sender to thereceiver upon receipt of the confirmation in step b), thereby using asecond redundancy version for representation of the information,selecting the redundancy version in dependence on a coding rate, andselecting a self-decodable redundancy version if the coding rate islower than a predefined upper coding rate.
 2. The method according toclaim 1, wherein the initially transmitted information is represented bythe first, self-decodable redundancy version and a first rate matchingpattern selected from a set of at least two self decodable rate matchingpatterns which are determined by a redundancy version parameterindicating a rate matching pattern.
 3. The method according to claim 2,wherein step c) further comprises selecting a further rate matchingpattern using the redundancy version parameter, which further ratematching pattern is different to that used in the first data packet. 4.The method according to claim 1, which further comprises a step ofretransmitting the information at least a second time in a third datapacket from the sender to the receiver upon receipt of a furtherconfirmation confirming an incorrect receipt from the receiver to thesender, thereby using a third redundancy version in dependence on acoding rate, and selecting a self-decodable redundancy version if thecoding rate is higher than the predefined upper coding rate andselecting a rate matching pattern using the redundancy versionparameter, which rate matching pattern is different from the first ratematching pattern used in the first data packet and the same as thefurther rate matching pattern used in the second data packet.
 5. Themethod according to claim 1, wherein the predefined upper coding rate isequal to 1/2.
 6. The method according to claim 1, wherein the step ofselecting in step c) is based on a puncturing parameter describingwhether the redundancy version has been produced with or without apuncturing of the bit sequence.
 7. The method according to claim 1,wherein the step of selecting in step c) is based on a transmissionnumber parameter describing a number n of retransmissions of informationin an n^(th) data packet.
 8. The method according to claim 7, wherein aset of redundancy versions can be derived from the bit sequence, andwherein a first subset of the set of redundancy versions is availablefor a first range of numbers of transmissions and a further subset ofthe set of redundancy versions is available for a further range ofnumbers of transmissions.
 9. The method according to claim 8, whereinthe first subset and the second subset are partly distinct from oneanother.
 10. The method according to claim 8, wherein the first subsetand the second subset are completely distinct from one another.
 11. Themethod according to claim 8, wherein the further subset of the set ofredundancy versions is a superset of the first subset.
 12. The methodaccording to claim 1, which comprises sending at least oneretransmission of the first information content, determining a number ofinformation contents sent in parallel, and using the number as a processnumber parameter for selecting the redundancy version.
 13. The methodaccording to claim 12, which comprises combining at least two parametersto obtain a further parameter.
 14. The method according to claim 1,wherein further a control confirmation indicating incorrect decoding ofa redundancy version is foreseen and, upon receiving a controlconfirmation, resetting a retransmission number to an original value.15. The method according to claim 1, which comprises describing theredundancy version by a parameter s, wherein the parameter s denoteswhether or not the redundancy version is self-decodable.
 16. Atelecommunications device, comprising means for performing the methodaccording to claim 1.